SOME p-BLOCK ELEMENTS

26. Classify the following oxides as neutral, acidic, basic, & amphoteric. Tl2O3, CO, B2O3, SiO2, CO2, Al2O3 Ans:- Neutral:- CO Acidic:- B2O3, SiO2, CO2 Amphoteric:- Al2O3 Basic:- Tl2O3

27. In some of reactions, thallium resembles aluminium, whereas in some others it resembles with group I metals. Support this statement by giving some evidences. Ans:- Aluminium shows a uniform oxidation of +3. Like aluminium, Tl also shows oxidation state of +3 in some of its compounds like TiCl3, Tl2O3, etc. like Al, Tl also forms octahedral complexes : [AlF6]3- and [Tif6]3-. Group 1 metals shows a oxidation state of +1. Like group 1 metals, Tl due to inert pair effect also shows +1 oxidation state in some of its compounds like Tl2O, TlCl, TlClO4, etc.

28. When metal X is treated with Naoh a white ppt 28. When metal X is treated with Naoh a white ppt. (A) is obtained, which is soluble in excess of NaOH to give a soluble complex (B). compound (A) is soluble in dil. HCl to form compound (C). the compound (A) when heated strongly give (D), which is used to extract metals. Indentify all the compounds. Ans:- Since metal (X) reacts with NaOH to first give white ppt. (A) which dissolves in excess of NaOH to give soluble complex (B), therefore metal (X) must be Al; ppt (A) must be Al(OH)3 and complex (B) must be Na+[Al(OH)4]- 2Al + 3NaOH  Al(OH)3 + 3Na+ Al(OH)3 + NaOH  Na+[Al(OH)4]- Since (A) is amphoteric in nature, it reacts give dil. HCl to form (C) must be AlCl3 Al(OH)3 + 3HCl  AlCl3 + 3H2O Since (A) on heating given (D) which is used to extract metal, therefore (D) must be Al2O3 2Al(OH)3  Al2O3 + 3H2O

29. What do you understand by the following:- Ans:- Inert pair effect:- as we move down the group the tendency of s-electrons to participate in bond formation decreases. This effect is known as inert pair effect. Allotropy:-the phenomenon of existence of elements in two or more forms which have different physical properties but same chemical properties is called allotropy. Catenation:-ability of like atoms to link one another through covalent bonds.

30.A certain salt X, gives the fol. Results: (i) its aq. Is alkaline to litmus (ii) it swells up to glassy material Y on strong heating (iii) when conc. H2SO4 is added to hot solution of X, white crystal of acid Z separates out. Write eqns. For all above reactions and identify X,Y,Z. Ans:- Na2B4O7.10H2O  2NaOH + H2B4O7 + 8H2O Na2B4O7.10H2O  Na2B4O7 + 10H2O Na2B4O7  2NaBO2 + B2O3 Na2B4O7.10H2O + H2SO4  4H3BO3 + Na2SO4 + 5H2O

31write the balanced equations for: (i) BF3 + LiH  (ii) B2H6 + H2O  (iii) NaH + B2H6  (iv) H3BO3 (v) Al + NaOH  (vi) B2H6 + NH3 Ans:- 2BF3 +6LiH  B2H6 + 6LiF B2H6 + 6H2O  2 H3BO3 + 6H2 2NaH + B2H6 2Na+[NH4]- H3BO3  HBO2 + H2O 2Al + 2NaOH  2Na+[Al(OH)4]- + 3H2 B2H6 +2NH32BH3.NH3

32. Give one method for industrial and laboratory preparation of CO and CO2 each. Ans:- Industrial : 2C + O2  2CO; C + O2  CO2 Laboratory: HCOOH  CO + H2O; CaCO3 + 2HCl  CaCl2 + CO2 + H2O 33. An aq. Sol. Of Borax is: (a) neutral (b)amphoteric (c) basic (d) acidic Ans:- (c)

34. Boric acid is polymeric due to : (a) its acidic nature (b)the presence of hydrogen bonds (c) its monobasic nature (d) its geometry Ans:- (b) 35. The type of hybridization of boron in diborane is (a) sp (b) sp2 (c) sp3 (d)dsp2 Ans:- (c)

36. Thermodynamically the most stable form of carbon is: (a) diamond (b) graphite (c) fullerenes (d)coal Ans:- (b) 37. Elements group 14. (a)exhibits oxidation state of +4 only (b) exhibit oxidation state of +2 and +4 (c) forms M2- and M4- ion (d) form M2+ and M4+ ions

THANK YOU